1. Field of the Invention
The present disclosure relates to a centrifugal pump, and more particularly, to a low specific speed centrifugal pump for use in conjunction with a fuel metering unit for a gas turbine engine.
2. Background of the Disclosure
Pumps have been widely used and are well understood in the art. They are utilized in a variety of applications such as petroleum refining plants and combustion engines. In use, pumps increase the flow and/or pressure of a fluid within a system in order to adequately supply a device which requires fluid with an increased fluid flow and/or pressure.
The present disclosure involves booster pumps. The term xe2x80x9cboosterxe2x80x9d is used to describe various applications. A xe2x80x9cbooster stagexe2x80x9d may mean a separate secondary pump on the inlet of a primary pump to further increase the net positive suction head (hereinafter xe2x80x9cNPSHxe2x80x9d) to the inlet of the primary pump. Traditionally, one employed low specific speed centrifugal pumps as the xe2x80x9cboost stagexe2x80x9d of a fuel metering unit for small gas turbine engines. Such centrifugal pumps are typically low speed (e.g., 6,000-12,000 rpm) and low volumetric flow, yet the boost stage must produce a relatively high pressure rise (e.g., 200 psid). A xe2x80x9cboosterxe2x80x9d may also refer to a suction device, such as an inducer, incorporated as part of a primary pump to improve its NPSH. Further, a secondary pump or impeller downstream and in series with the primary pump to increase discharge pressure is also called a xe2x80x9cboosterxe2x80x9d.
Several systems have been developed to more efficiently and cost effectively energize a fluid pathway. For example, U.S. Pat. No. 5,779,440 to Stricker et al. discloses means for forming jet sheets upstream of an impeller. The device includes a recirculation chamber surrounding an impeller shroud for recirculating fluid back through the impeller. It is also common for pumps to have multiple impellers in series which move the same fluid, e.g., xe2x80x9cmulti-stagexe2x80x9d pumps. Multistage pumps further increase the flow and pressure of fluid. U.S. Pat. No. 5,599,164 to Murray shows a multi-stage centrifugal pump assembly including primary and booster impellers, wherein the inlet of the secondary impeller is connected to the outlet of the primary impeller.
Despite their utility, there are disadvantages associated with these prior art systems. For example, multiple impellers increase cost, complexity and require additional drive mechanism horsepower. Additional complexity involves more costly maintenance creating an undesirably high cost of ownership. Prior art pumps are inefficient. Pump efficiency is the pump output in terms of liquid horsepower compared to the horsepower delivered to the drive shaft. Seal and windage loss decrease efficiency. Seal loss is the fluid leakage from higher pressurized areas to lower pressurized areas. Windage, the drop in efficiency due to impeller friction, is the predominant type of loss in many pumps. In particular, relatively large diameter impellers and relatively narrow width impeller blades which are necessary to achieve the desired performance increase windage which reduces efficiency. In addition, temperature increases for the fluid can occur as the fluid is pumped through the fluid. In many instances, such temperature increases are undesirable.
In view of the foregoing deficiencies, there is a need for a compact, lightweight, economical and reliable low specific speed centrifugal pump with improved efficiency, and which does not increase the temperature of the fluid pumped thereby.
The present invention provides a centrifugal pump for a gas turbine engine, including a housing having a fluid inlet port for receiving fluid at an initial pressure and an interior chamber defining a central axis. An impeller disk disposed within the interior chamber of the housing and mounted for rotation about the central axis. The impeller disk defines first and second inlet areas and has a plurality of circumferentially spaced apart channels formed therein which extend from the inlet areas for conducting fluid from the inlet areas in a radially outward direction upon rotation of the impeller disk so as to increase the pressure of the fluid. A first collector is formed by the housing for receiving the fluid from the first inlet area via the channels at a first elevated pressure relative to the initial pressure and a second collector is formed by the housing for receiving fluid from the second inlet area via the channels at a second elevated pressure relative to the first elevated pressure. A cross-over conduit is formed by the housing for conducting fluid from the first collector to the second inlet area of the impeller disk and an outlet is formed by the housing for conducting fluid from the second collector.
Preferably, the plurality of circumferentially spaced apart channels are bifurcated adjacent an outer diameter of the impeller and the impeller is configured in such a manner so that at least seventy percent of the circumferentially spaced apart channels are in fluid communication with the first and second inlet areas. In yet another embodiment, the first collector and the second collector are diametrically opposed from one another relative to the central axis of the housing.
In another embodiment, the housing further defines sealing lands with the impeller disk for sealingly isolating the first and second collectors. In another embodiment, the impeller disk may be shrouded, unshrouded or open. The plurality of circumferentially spaced apart channels are preferably adapted and configured to facilitate fluid communication between the first inlet area and the first collector, and between the second inlet area and the second collector.
Still another embodiment of the present invention includes a device which comprises an inducer, having a helical blade extending radially outward, rotatably mounted about the central axis of the housing for drawing fluid axially from the fluid inlet port to the first inlet area of the impeller disk.
And yet another embodiment of the present invention includes a housing with a partition within the interior chamber for isolating the first inlet area from the second inlet area. Preferably, the partition defines a third inlet area, the outlet conducts fluid from the second collector to the third inlet area and the housing defines a third collector outward of the impeller for receiving the fluid passed through the impeller from the third inlet area and a second outlet formed by the housing for conducting fluid from the third collector. It is also envisioned that a first elevated pressure outlet may be provided for conducting the fluid from the first collector to allow the centrifugal pump to supply the fluid at the first elevated pressure and the second elevated pressure.